This invention relates generally to optical reproducing apparatus and, more particularly, is directed to optical reproducing apparatus of the type adapted to rapidly move an optical pickup device thereof to a desired position on a record disc during a search operation.
Apparatus is known in the art for optically reproducing an information signal, such as a frequency modulated (FM) video signal or a pulse code modulated (PCM) audio signal, from a record disc during rotation of the latter. With such apparatus, an optical pickup device is positioned below the record disc and projects a laser beam onto the disc. The laser beam is modulated by the information recorded on the disc in the form of small pits arranged in a spiral track or in concentric tracks, and the modulated laser beam is reflected from the underside of the disc back to the optical pickup device which produces an output signal in response to the modulated laser beam and which supplies such signal to further processing circuitry for separating the information therefrom.
The optical pickup device generally includes an objective lens which is movable in the direction of its optical axis toward or away from the record disc to focus the projected laser beam onto the record disc. A lens driving mechanism is also provided for applying an electromagnetic force, in response to the unfocused condition of the modulated laser beam reflected from the disc, to move the objective lens in the direction of its optical axis and thereby provide a focusing servo control arrangement for maintaining correct focus of the laser beam projected onto the record disc. In order to provide correct tracking of the laser beam onto the center of each record track, a movable mirror is interposed in the path of the light beam projected onto the disc for deflecting the light beam in a direction transverse to each respective record track so that the laser beam is always projected onto the center of each record track. During the normal reproducing mode of operation of the optical reproducing apparatus, a tracking error signal is produced in response to the modulated laser beam reflected from the record disc. A mirror driving mechanism applies an electromagnetic force to the movable mirror, in response to the tracking error signal, to provide a tracking servo control arrangement for maintaining correct tracking of each respective record track by the optical pickup device.
In addition, a drive mechanism is provided for moving the optical pickup device linearly in the radial direction of the record disc, that is, in a direction transverse to the record tracks, from the inner or outer periphery of the record disc in correspondence with rotation thereof. For example, the drive mechanism may comprise suitable gearing and a drive motor. Thus, the drive mechanism continuously moves the optical pickup device in the radial direction of the record disc as the latter is rotated at a predetermined constant linear velocity or a predetermined constant angular velocity, whereby the optical pickup device continuously scans the record tracks of the record disc.
It has been proposed to also detect address information recorded on the record disc for performing a search or track jump operation so that reproduction at a desired position can be easily and quickly achieved. In particular, a selected address corresponding to the desired position is preset, and the drive mechanism is controlled by a track jump signal to move the pickup device rapidly across the record tracks to the desired position on the record disc corresponding to the selected address. In addition to, or alternatively, during the search mode of operation, the mirror driving mechanism may generate another electromagnetic force, in response to the track jump signal, to control the movable mirror to rapidly move the projected laser beam across a plurality of record tracks to the desired position on the record disc.
However, it is to be appreciated that, during such rapid movement of the projected laser beam across or transverse to the record tracks, a large forcusing error is detected. In response thereto, the aforementioned focus servo control arrangement responds to detected rapid variations in the focused state of the laser beam reflected from the record disc to control the objective lens so that the latter rapidly moves or oscillates toward and away from the record disc to compensate for such detected variations. As a result, a large vibratory movement of a portion of the structure supporting the objective lens occurs, resulting in a harsh noise being produced by the objective lens.